1. Field of the Invention
The present invention relates to a technology for controlling a light emitting unit, and more particularly, to a back light module utilizing a dithering scheme to drive a plurality of light emitting units, and a related driving method.
2. Description of the Prior Art
Light emitting diodes (LEDs) used as light sources have become popular in recent years. For example, the light source in a back light module of a conventional liquid crystal display (LCD) panel is usually a plurality of cold cathode fluorescent lamps (CCFLs). However, as the luminous efficiency of an LED increases and the cost of LEDs decreases, CCFLs are gradually being replaced by LEDs as the light source in a back light unit.
The LED back light module is implemented with a driving scheme of controlling divided areas. In other words, the LCD panel and the LED back light are divided into a plurality of areas, wherein each area of the LCD panel corresponds to each area of the LED back light unit. Please refer to FIG. 1. FIG. 1 is a diagram of a conventional back light module 100 of an LCD. As shown in FIG. 1, the back light module 100 includes a plurality of LEDs 110, a timing controller 120, a pulse width modulation (PWM) controller 130, and a plurality of switches 140. The timing controller 120 outputs a control signal SC according to the peak values of the gray levels in different areas of the LCD panel. The PWM controller 130 is electrically connected to the timing controller 120 and utilized for controlling an on/off state of the switches 140 according to the control signal Sc in order to adjust the luminance of each area of the LEDs 110.
In prior art schemes, the back light module utilizes high power LEDs. If the luminance of an LED is divided into 17 (i.e. 42+1) levels, the PWM controller 130 has to transmit a 4-bit control signal to control the LED. Thus, the data transmission quantity will increase when the LED has more luminance levels. In addition, there is a problem of overheating of the LEDs due to the LEDs usually emitting light for a long time. If one of the LEDs fails, it will result in the whole light source being of unstable quality.